A conventional band saw is often used in sawmills. Such a band saw typically has a relatively large, circular, band saw blade, mounted along the path of travel of a log placed on a suitable moving bed with a drive mechanism for advancing the log against the blade. Alternatively, the log remains stationary and the band saw is mounted on a carriage which is capable of transverse displacement along the log.
One problem faced with band saws having large band saw blades is the tensioning of said blade. The blade moves in a generally circular path, typically around two band wheels, one of which is powered by a motor, either via direct drive or a belt drive. The portion of the saw blade between the two band wheels is often exposed and largely unrestrained; complex forces on the blade as it passes through the log result in substantial and undesired transverse motion of the blade, resulting in reduction in efficiency, reduction in accuracy of the cut, and an increase in wear on the saw blade and sometimes its drive assembly and motor.
In order to counteract such forces, various mechanisms are used. For example, a blade tensioning system may be used to provide increased tension on the blade.
This will help restrict transverse motion, but often at the cost of added parts, and an increase in tension (and a resulting increase in wear) on the band wheels. Another example of a mechanism used to decrease transverse motion on the blade is the use of one or more blade guides which act to guide the blade. Typically, a blade guide will be rigidly affixed to the band saw, and extend into, or immediately proximal to, the path of the blade. A blade guide will often have an upper and a lower jaw and rear thrust plate, each having roller wheels or other low friction running surface, or alternatively, one-sided support surface and rear thrust plate. The flat portion of the blade, or in the alternative, the straight edge of the blade, will travel along the roller wheels. Since the blade guide is affixed to the band saw, it helps prevent transverse motion while minimally affecting the desired rotatory blade motion.
There are several prior inventions for band saws.
U.S. Pat. No. 4,275,632 describes a portable sawmill comprising a U-shaped support or carriage, holding a band saw. When in use, a log is placed between the two guide rails and is supported in place by a jacking mechanism with adjustable shelves. The band saw is in a generally horizontal position (though with one end slightly elevated), and does not adjust in a vertical direction; instead, the log itself is moved up and down using a jacking mechanism. The patent describes a blade tensioning system as well as guide rollers. The guide rollers engage the straight edge of the band saw as an aid in holding the band saw in position on the wheel.
Canadian Patent No. 1,200,180 describes a portable sawmill having a band saw on a carriage. The carriage is moveable along the guide rail along two sets of wheels, one engaged with the upper side of the guide rail and the other with the lower side. The band saw comprises a circular band saw blade which travels along two band saw wheels. The band saw has a stationary blade guide, having a set of blade guide wheels, guides the blade on the lower drive side. The band saw also has a movable blade guide, having a set of blade guide wheels, on the driven side. The movable blade guide allows for adjustment of the length of the exposed cutting section of the blade. The adjustable blade guide is attached to a telescopic guarded tube arrangement which protects a portion of the blade. The adjustable blade guide is adjusted through a screw and nut “T” handle, which allows tightening of the assembly. To adjust the adjustable blade guide, one unscrews the screw on the T handle, then moves the blade guide to the desired position. Then one tightens the screw on the T handle, affixing the blade guide in position.
The LumberMate™ band sawmill (http://www.norwoodindustries.com) is a portable sawmill having a band saw with a circular band saw blade which rotates around two band saw wheels. The band saw has a stationary blade guide, having a set of blade guide wheels, guides the blade on the lower drive side. The band saw also has a movable blade guide, having a set of blade guide wheels, on the driven side. The movable blade guide allows for adjustment of the length of the exposed cutting section of the blade. Similarly to the blade guide described in CA 1,200,180, the adjustable blade guide is adjusted through a screw and nut “T” handle, which allows tightening of the assembly. To adjust the adjustable blade guide, one unscrews the screw on the T handle, then moves the blade guide to the desired position. Then one tightens the screw on the T handle, affixing the blade guide in position.
There is a need for an improved portable sawmill having an adjustable blade guide that is easy to adjust and self locking.